WO2021124203A1 - Feuille d'acier laminée à chaud et traitée thermiquement et procédé de fabrication de cette dernière - Google Patents

Feuille d'acier laminée à chaud et traitée thermiquement et procédé de fabrication de cette dernière Download PDF

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Publication number
WO2021124203A1
WO2021124203A1 PCT/IB2020/062116 IB2020062116W WO2021124203A1 WO 2021124203 A1 WO2021124203 A1 WO 2021124203A1 IB 2020062116 W IB2020062116 W IB 2020062116W WO 2021124203 A1 WO2021124203 A1 WO 2021124203A1
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WIPO (PCT)
Prior art keywords
steel sheet
martensite
hot rolled
heat
temperature
Prior art date
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PCT/IB2020/062116
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English (en)
Inventor
Astrid Perlade
Kangying ZHU
Coralie JUNG
Frédéric KEGEL
Original Assignee
Arcelormittal
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Arcelormittal filed Critical Arcelormittal
Priority to CN202080074063.5A priority Critical patent/CN114585763A/zh
Priority to US17/784,922 priority patent/US20230032122A1/en
Priority to EP20825270.0A priority patent/EP4077745A1/fr
Priority to UAA202202321A priority patent/UA127583C2/uk
Priority to JP2022532077A priority patent/JP2023506395A/ja
Priority to MX2022007461A priority patent/MX2022007461A/es
Priority to KR1020227016274A priority patent/KR20220083776A/ko
Priority to CA3157208A priority patent/CA3157208C/fr
Publication of WO2021124203A1 publication Critical patent/WO2021124203A1/fr
Priority to ZA2022/03670A priority patent/ZA202203670B/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B2001/225—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by hot-rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a hot rolled and heat-treated high strength steel sheet having high ductility and to a method to obtain such steel sheet.
  • the publication WO2019123245 describes a method to obtain a high strength and high formability cold rolled steel sheet with a yield strength YS comprised between 1000 MPa and 1300 MPa, a tensile strength TS comprised between 1200 MPa and 1600 MPa, a uniform elongation UE of at least 10%, a hole expansion ratio HER of at least 20%, thanks to a quenching & partitioning process.
  • the microstructure of the cold rolled steel sheet consists of, in surface fraction: between 10% and 45% of ferrite, having an average grain size of at most 1.3 pm, the product of the surface fraction of ferrite by the average grain size of the ferrite being of at most 35 pm%, between 8% and 30% of retained austenite, said retained austenite having an Mn content higher than 1 .1 * Mn%, Mn% designating the Mn content of the steel, at most 8% of fresh martensite, at most 2.5% of cementite and partitioned martensite.
  • the hot rolled steel sheet has to be annealed a first time, cold rolled, and annealed a second time before the quenching and the partitioning steps.
  • Those processes, and in particular the second annealing allow to control the Mn content in the retained austenite, to obtain a combination of high ductility and high strength, but complicates the manufacturing process.
  • the purpose of the invention therefore is to provide a hot rolled steel sheet having yield strength YS higher than 950MPa, tensile strength TS higher than 1180MPa, a uniform elongation UE higher than 10% and a hole expansion ratio HER higher than 25% and easily processable on conventional process route.
  • the object of the present invention is achieved by providing a steel sheet according to claim 1 .
  • the steel sheet can also comprise characteristics of anyone of claims 2 to 8. Another object is achieved by providing the method according to claim 9. Another object of the invention is achieved by providing a steel sheet according to claim 10.
  • Ae1 designates the equilibrium transformation temperature below which austenite is completely unstable
  • Ae3 designates the equilibrium transformation temperature above which austenite is completely stable
  • Ms designates the martensite start temperature, i.e. the temperature at which the austenite begins to transform into martensite upon cooling and Tnr the temperature of non-recrystallization.
  • Ae3 890 - 20 * V%C + 20 * %Si - 30 * %Mn + 130 * %AI
  • composition of the steel according to the invention comprises, by weight percent:
  • the carbon content is comprised between 0.12% and 0.25 %. Above 0.25% of addition, weldability of the steel sheet may be reduced. If the carbon content is lower than 0.12%, the retained austenite fraction is not stabilized enough to obtain a sufficient elongation. In a preferred embodiment, the carbon content is comprised between 0.15% and 0.25%.
  • the manganese content is between 3.0% and 8.0 % to obtain sufficient elongation with the stabilization of the austenite. Above 8.0% of addition, the risk of central segregation increases to the detriment of the yield strength and the tensile strength. Below 3.0%, the final structure comprises an insufficient retained austenite fraction, so that the desired combination of ductility and strength is not achieved.
  • the manganese content is comprised between 3.0% and 4.4%. In an other preferred embodiment, the manganese content is comprised from 3.0% to 4.3%. In an other preferred embodiment, the manganese content is comprised from 3.0% to 4.2%. In an other preferred embodiment, the manganese content is comprised from 3.0% to 4.1%. In an other preferred embodiment, the manganese content is comprised from 3.0% to 4.0%.
  • the silicon content according to the invention is comprised between 0.7% and 1 .5%.
  • a silicon addition of at least 0.7% helps to stabilize a sufficient amount of retained austenite. Above 1.5%, silicon oxides form at the surface, which impairs the coatability of the steel.
  • the silicon content is comprised between 0.8% and 1 .3%.
  • the aluminium content is comprised between 0.3% and 1 .2%. Aluminium is a very effective element for deoxidizing the steel in the liquid phase during elaboration. The aluminium content is not higher than 1 .2% to avoid the occurrence of inclusions and to avoid oxidation problems. In a preferred embodiment, the aluminium content is comprised between 0.3% and 0.8%.
  • the boron content is comprised between 0.0002% and 0.004 % to increase the quenchability of the steel and to improve the weldability.
  • some elements can be added to the composition of the steel according to the invention:
  • Niobium can be optionally added up to 0.06 % to refine the austenite grains during hot-rolling and to provide precipitation strengthening.
  • the minimum amount of niobium added is 0.0010%. Above 0.06%, yield strength and elongation are not secured at the desired level.
  • Molybdenum can be optionally added up to 0.5 %. Molybdenum stabilizes the retained austenite thus reducing austenite decomposition during partitioning. Above 0.5%, the addition of molybdenum is costly and ineffective in view of the properties which are required.
  • Vanadium can be added up to 0.2 % in order to provide precipitation strengthening. Titanium can be added up to 0.05 % to provide precipitation strengthening. If the titanium level is above or equal to 0.05%, yield strength and elongation are not secured at the desired level. Preferably a minimum of 0.01% of titanium is added in addition of boron to protect boron against the formation of BN.
  • the remainder of the composition of the steel is iron and impurities resulting from the smelting.
  • P, S and N at least are considered as residual elements which are unavoidable impurities.
  • Their content is less than 0.010 % for S, less than 0.020 % for P and less than 0.008 % for N.
  • the hot rolled and heat-treated steel sheet has a microstructure consisting of, in surface fraction, between 5% and 45% of ferrite, between 25% and 85% of partitioned martensite, said partitioned martensite having a carbides density less than 2x10 6 /mm 2 , between 10% and 30% of retained austenite, less than 8% of fresh martensite, a part of fresh martensite being combined with retained austenite to form martensite-austenite (M-A) islands in total surface fraction of less than 10%, and a pancaking index lower than 5.
  • M-A martensite-austenite
  • the microstructure of the hot-rolled and heat-treated steel sheet comprises between 5% and 45% ferrite.
  • This ferrite is formed during the annealing between (Ae1 +Ae3)/2 and Ae3. Below 5% of ferrite fraction, the uniform elongation does not reach 10%. If the ferrite fraction is higher than 45%, the tensile strength of 1180MPa and the yield strength of 950MPa are not achieved.
  • the microstructure comprises 10% or more of ferrite. More preferably, the microstructure comprises 15% or more of ferrite.
  • the microstructure of the hot-rolled and heat-treated steel sheet comprises between 25% and 85% of partitioned martensite, to ensure high ductility of the steel.
  • Partitioned martensite is the martensite formed upon cooling after the annealing then partitioned during the partitioning step.
  • Said partitioned martensite has a carbides density less than 2x10 6 /mm 2 .
  • the low density of carbides inside partitioned martensite ensures a combination of good level of tensile strength and elongation.
  • the microstructure of the hot-rolled and heat-treated steel sheet comprises between 10% and 30% of retained austenite, to ensure high ductility of the steel and less than 8% of fresh martensite. Fresh martensite is formed during the cooling to room temperature of the hot rolled and heat-treated steel sheet.
  • M-A martensite- austenite
  • the microstructure of the hot-rolled and heat-treated steel sheet has pancaking index lower than 5.
  • the pancaking index is defined as the ratio of the prior austenite grain size in the rolling direction PAGSroii over the prior austenite grain size in the normal direction PAGSnorm.
  • PAGSroii is the maximum length of prior austenite grain in rolling direction.
  • PAGSnorm is the maximum length of prior austenite grain in normal direction.
  • the steel sheet according to the invention can be produced by any appropriate manufacturing method and the man skilled in the art can define one. It is however preferred to use the method according to the invention comprising the following steps:
  • a semi-product able to be further hot-rolled is provided with the steel composition described above.
  • the semi product is heated to a temperature Treheat comprised between 1150°C and 1300°C, so to make it possible to ease hot rolling, with a final hot rolling temperature FRT comprises between Tnr-100°C and 950°C, to obtain a hot rolled steel sheet.
  • Treheat comprised between 1150°C and 1300°C
  • FRT comprises between Tnr-100°C and 950°C
  • FRT is higher than Tnr-100°C to generate a microstructure with a prior austenite grain pancaking index lower than 5, the pancaking index being defined as the ratio of the PAGSroii over PAGSnorm.
  • pancaking index is higher than 5, the hole expansion ratio cannot be at the target.
  • the hot-rolled steel is then cooled and coiled at a temperature Tcoii comprised between 20°C and 700°C.
  • the coiling temperature is comprised from 20°C to 550°C.
  • the sheet After the coiling, the sheet can be pickled to remove oxidation.
  • the microstructure of the hot rolled and coiled steel sheet comprises martensite and bainite the sum of which being higher than 80%, strictly less than 20% of ferrite and strictly less than 20% of the sum of martensite-austenite (M-A) islands and carbides, and has the multiplication of PAGSroii by PAGSnorm lower than 1000pm 2 , and the pancaking index lower than 5.
  • the microstructure after the coiling and the cooling comprises less than 10% of ferrite, and more preferably no ferrite.
  • the microstructure after the coiling and the cooling comprises less than 10% of the sum of M-A islands and carbides.
  • the martensite of M-A islands is fresh martensite formed during final cooling.
  • the determination of the type of martensite can be done and quantify thanks to a Scanning Electron Microscope.
  • the hot rolled steel sheet then undergoes a quenching and partitioning process (Q&P).
  • the quenching and partitioning process comprises the steps of:
  • the hot-rolled and heat treated steel sheet according to the invention has tensile strength TS higher than 1180 MPa, a yield strength YS higher than 950 MPa, a uniform elongation UE higher than 10%, and a hole expansion ratio HER higher than 25%.
  • TS, YS, UE and the total elongation TE are measured according to ISO standard ISO 6892-1 .
  • HER is measured according to ISO standard ISO 16630.
  • the hot rolled and heat-treated steel sheet according to the invention has TS and YS expressed in MPa, UE, TE and HER, expressed in %, satisfying the following formula: YS * UE+TS * TE+TS * HER >65000.
  • the total elongation TE is higher than 14%.
  • the tested composition is gathered in the following table wherein the element contents are expressed in weight percent.
  • the surface fractions are determined through the following method: a specimen is cut from the hot-rolled and heat-treated, polished and etched with a reagent known per se, to reveal the microstructure. The section is afterwards examined through optical or scanning electron microscope, for example with a Scanning Electron Microscope with a Field Emission Gun (“FEG-SEM”) at a magnification greater than 5000x, coupled to a BSE (Back Scattered Electron) device.
  • FEG-SEM Field Emission Gun
  • the determination of the surface fraction of each constituent are performed with image analysis through a method known per se.
  • the retained austenite fraction is for example determined by X-ray diffraction (XRD).
  • XRD X-ray diffraction
  • PAGS in rolling direction (RD) PAGSroii and in normal direction (ND) PAGSnorm are determined through the following method: a specimen is cut from the hot-rolled sheet, polished and etched with a reagent known per se, to reveal the microstructure especially the prior austenite grain boundaries.
  • the section of RD-ND plane is afterwards examined through optical or scanning electron microscope, for example with a Scanning Electron Microscope at a magnification of 1000x to 5000x.
  • the maximum lengths of prior austenite grains in RD and in ND are measured.
  • n.a non-assessed values y: stands for residual austenite surface fraction PM: stands for partitioned martensite surface fraction FM: stands for fresh martensite surface fraction B: stands for bainite surface fraction F: stands for ferrite surface fraction MA: stands for martensite-austenite islands surface fraction
  • the examples 1 and 3 according to the invention show all the targeted properties thanks to their specific composition and microstructures.
  • the steel sheet is annealed and cold rolled before the Q&P process.
  • the microstructure before Q&P is then 80% ferritic, leading to a high content of fresh martensite after Q&P. This high fraction of large-sized fresh martensite leads to a hole expansion ratio lower than 25%.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

L'invention concerne une feuille d'acier laminée à chaud et traitée thermiquement présentant une composition comprenant, en pourcentage en poids : C de 0,12 à 0,25 %, Mn de 3,0 à 8,0 %, Si de 0,70 à 1,50 %, Al de 0,3 à 1,2 %, B de 0,0002 à 0,004 %, S ≤ 0,010 %, P ≤ 0,020 %, N < 0,008 %, le reste de la composition étant du fer et des impuretés inévitables résultant de la fusion, et présentant une microstructure constituée de, en fraction de surface : entre 5 % et 45 % de ferrite, entre 25 % et 85 % de martensite fractionnée, ladite martensite fractionnée présentant une densité de carbures inférieure à 2x106 /mm2, entre 10 % et 30 % d'austénite résiduelle, moins de 8 % de martensite fraîche, une partie de ladite martensite fraîche étant combinée avec de l'austénite résiduelle sous la forme d'îlots martensite-austénite dans une fraction de surface totale inférieure à 10 %, et un indice d'aplatissement inférieur à 5.
PCT/IB2020/062116 2019-12-19 2020-12-17 Feuille d'acier laminée à chaud et traitée thermiquement et procédé de fabrication de cette dernière WO2021124203A1 (fr)

Priority Applications (9)

Application Number Priority Date Filing Date Title
CN202080074063.5A CN114585763A (zh) 2019-12-19 2020-12-17 经热轧和热处理的钢板及其制造方法
US17/784,922 US20230032122A1 (en) 2019-12-19 2020-12-17 Hot rolled and heat-treated steel sheet and method of manufacturing the same
EP20825270.0A EP4077745A1 (fr) 2019-12-19 2020-12-17 Feuille d'acier laminée à chaud et traitée thermiquement et procédé de fabrication de cette dernière
UAA202202321A UA127583C2 (uk) 2019-12-19 2020-12-17 Гарячекатаний та термооброблений сталевий лист і спосіб його виготовлення
JP2022532077A JP2023506395A (ja) 2019-12-19 2020-12-17 熱間圧延熱処理鋼板及びその製造方法
MX2022007461A MX2022007461A (es) 2019-12-19 2020-12-17 Hoja de acero laminada en caliente y tratada termicamente y metodo de fabricacion de la misma.
KR1020227016274A KR20220083776A (ko) 2019-12-19 2020-12-17 열간 압연 및 열처리된 강판 그리고 이의 제조 방법
CA3157208A CA3157208C (fr) 2019-12-19 2020-12-17 Feuille d'acier laminee a chaud et traitee thermiquement et procede de fabrication de cette derniere
ZA2022/03670A ZA202203670B (en) 2019-12-19 2022-03-30 Hot rolled and heat-treated steel sheet and method of manufacturing the same

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US20230032122A1 (en) 2023-02-02
UA127583C2 (uk) 2023-10-18
CN114585763A (zh) 2022-06-03
CA3157208A1 (fr) 2021-06-24
WO2021123889A1 (fr) 2021-06-24
JP2023506395A (ja) 2023-02-16
MX2022007461A (es) 2022-06-27
ZA202203670B (en) 2022-10-26
KR20220083776A (ko) 2022-06-20
CA3157208C (fr) 2024-03-05

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